The magnetic phase transition near T0=8.5 K in americium dioxide (AmO2) has been investigated microscopically by means of O17 NMR. To avoid complexities arising from sample aging associated with the α decay of Am243, all measurements have been performed within 40 days after sample synthesis. Even during such a short period, however, a rapid change of NMR line shape has been observed at 1.5 K, suggesting that the ground state of AmO2 is very sensitive to disorder. We have also confirmed the loss of O17 NMR signal intensity over a wide temperature range below T0, and more than half of oxygen nuclei are undetectable at 1.5 K. This behavior reveals the persistence of slow and distributed spin fluctuations down to temperatures well below T0. In the paramagnetic state, strong NMR line broadening and spatially inhomogeneous spin fluctuations have been observed. The results are all indicative of short-range, spin-glass-like character for the magnetic transition in this system.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 2014 Jun 19|